I encountered a similar issue in the exact spot. Rather than being stuck however, I was able to run through the walls and stairs like the zombies used to do. My body was halfway through the floor. Going outside and walking back in on the steps would "reset" the character until standing in that same corner again.

EDIT:
Added two pictures:

2014-07-12_00004.jpg - Shows view from character which has "fallen" through the floor.
2014-07-12_00006.jpg - Shows view from character standing "inside" the central stairs.